1. Field of the Invention
The present invention relates to a Lactuca sativa cultivar exhibiting resistance to 17 known strains of Downy Mildew (Bremia lactucae), Corky Root (Rhizomonas suberifaciens) and Lettuce Mosaic Virus (LMV), partial resistance to Fusarium Wilt (Fusarium oxysporum f.sp. lactucae), combined with a fast growth and fast heartfilling.
2. Background of the Invention
Vegetables and especially lettuce have growing importance in the human diet. There are unique qualities to these foodstuffs that make them critically important to good health and longevity of life. Such vegetables are nearly exclusive eaten in their natural state as a fresh, raw product. As such the appearance of such vegetables is critical to their sale. Americans especially demand a perfect or near perfect appearance of their raw products. Whereas, in some countries, foodstuffs can have blemishes and imperfections and be fit for the market, the US consumer demands a perfect near unblemished product.
It will be appreciated that all growers are faced with a limited amount of space in which to grow their vegetables and food products. It is more than desirable to maximise the yield of a particular parcel and especially so for the small to moderate sized grower. For example, if a grower can break even by selling about 500 cartons of lettuce per acre and he can switch to a different variety of the same lettuce and grow about 900 cartons of lettuce per acre, the product of the different variety would be much more valuable. This very well could be the difference between a grower able to survive bad economic conditions one year and continue his operation or going under and being forced to sell out or turn his land into residential property.
The export of vegetables across the international and state lines is vital to the grower and shippers of fresh produce. In fact, California and Arizona grow about 90% of the total United States lettuce production and It is estimated that about 75% or more of all lettuce grown in California is so exported (Subbaroa 1998) for sale in states such as New York, Pennsylvania, Massachusetts and the like.
For a further understanding of lettuce, its uses and history Waycoft et al, U.S. Pat. No. 5,973,232 and Subbaroa 1998 is incorporated herein by references. There are six morphological types of lettuce: crisphead (iceberg), butterhead, Cos (Romaine), leaf, stem and Latin. The crisphead is the most common in the United States,just as Romaine types, while butterhead, iceberg and Romaine types are popular in northern and southern Europe. Cultivated lettuce originated from the ancestral wild species L. sativa. Today there are hundreds of cultivars, which are divided into four large groups based on morphological characteristics of the gross leaf morphology and leaf arrangement (Subbaroa 1998). These basic lettuce types frequently form the basis for grouping lettuces as is commonly seen in supermarkets, grocery and produce stores. Each of these basic groups is comprised of numerous cultivars; each characterised by its own particular morphology, disease resistance, and cultural adaptations.
Lettuce cultivars are susceptible to a number of diseases such as downy mildew (Bremia lactucae), lettuce drop (Sclerotinia minor and S. sclerotiorum), corky root (Rhizomonas suberifaciens), Fusarium Wilt, lettuce mosaic virus, big vein and aster yellows, just to list a few. These diseases result in millions of dollars of lost lettuce crop through the world every year.
The United States have a strict control on the presence of LMV on the seed of lettuce. The Salinas Valley Authority has designated a period in December that no lettuce plants may grow in the field. This will break the cycle of LMV in the field. Seed companies go through strict precocious measures to avoid that contaminated seed is planted in the United States. Varieties that have a genetic resistance against Lettuce Mosaic virus are not able to spread the disease. This reduces the cost of production for the seed company and reduces the risk of the unwanted importation of LMV to the United States.
Growers want to have a quick and reliable return on their investment in a lettuce crop. They want a variety that produces a good sized marketable head with an early filling of the heart, that reaches the minimum weight earlier. Not only to be able to sell their product earlier, but also to spend less on irrigation and pest- and disease-control during the time the crop is in the field.